Cosmopolis, Batboy and Rubin find themselves up against the Fugle Gang and Rubin panics. Batboy says they should run, but then realizes he has a vial of secret gas in his utility belt. He makes quick work of the villains and then the heroes depart in their Battlemobile. Rubin is confident that they've eliminated the person or persons responsible for the recent killing spree. However, he discovers a pair of gloves in the glove compartment... with a corpse inside. Batboy switches to the Battlecycle and they try to swing down on the ones responsible. They go through a wall and find themselves facing the Dead-End Kids, the Fleagle Gang. Batboy and Rubin run until Batboy realizes he has tiny hairbrushes hidden in his utility belt, and administers a series of spankings.

A page later, Batboy and Rubin swing across Cosmopolis and discover another victim fastened to their rope. They get to the Battle-Wagon and go after the Flurgle Gang, the only ones left who could be responsible. They swing through the wall to the hideout of the Flurgle Gang, a bevy of beautiful women. They try to wrestle with them but are quickly knocked down, and revert to nuclear weaponry. In the aftermath, Batboy and Rubin are confident there will be no more murders. They go back to their headquarters, only to discover another body. Rubin realizes that the villain can only be... Batboy, who knocks him down from behind. He removes Rubin's boots and explains that he made two punctures in each victim’s big toes, and sucked out the blood, because he is... Vampire Batboy! He proceeds to feed on Rubin...

Bat-Mite interrupts the adventure to explain that as an all-powerful fifth-dimensional being, he can view the adventures of an infinite number of different Batmans. He begins to tell the stories of Batman's Strangest Cases. He fast-forwards through the opening credits and then tells the tale of Bat-Manga.

In their last adventure, Batman and Robin triumphed over their archenemy, Lord Death Man. The heroes watch as Lord Death Man is buried, confident that there's no way that he could escape from the grave a second time. Everything goes dark and Batman finds himself facing Lord Death Man, who grows to giant size and releases his head to attack... and Bruce wakes up from his nightmare. He and Dick Grayson are attending Mr. Starr's party, and Mr. Starr introduces a swami who can be buried for an hour and survive without air. Sixty minutes later, Mr. Starr digs him up and reveals that the swami has survived. The swami explains that he uses a secret yoga method, and Batman realizes that Lord Death Man used the same method. They go to the graveyard and dig up Lord Death Man's coffin, and find it empty except for a note offering the coffin as a gift. Lord Death Man emerges and orders his men to emerge from the graves and open fire. Batman goes down in a hail of gunfire.

Batman falls into a grave and Lord Death Man orders his men to bury him. However, Batman swings out of the grave, knocks down the henchmen, and swings into the Batmobile. Robin disarms Lord Death Man and gets into the vehicle, and they lay down a cloud of smoke. Robin takes the wheel and swings the Batmobile around, allowing Batman to take out the henchmen. Lord Death Man takes off in a helicopter and drops bombs on them, and Robin activates the smokescreen. Lord Death Man flies into power lines and his helicopter explodes. Batman and Robin are confident that the villain parachuted away to safety despite his apparent death, and laugh in triumph.

Bat-Mite moves onto the third strange adventure, featuring Batman's team up with the greatest detective of all time: Scooby-Doo.

The Mystery Gang visits the theater where their favorite songster, Weird Al Yankovic, is scheduled to perform. The ticket girl is surprised that anyone would want to be there, says it's their funeral, and closes up. Inside, Weird Al is performing to an audience of two. The elderly stage manager explains to the gang that everyone else has been scared away by the Footlight Phantom. The ghostly villain appears on the stage and makes Weird Al disappear in a cloud of smoke. Fred snags the villain and they unmask him, and are surprised to discover that it's the Joker. The villain introduces his partner, the Penguin, and they prepare to dispose of the meddling kids.

The villains place the gang on one dish of a giant set of scales, positioned above a shark tank. Scooby-Doo is tied up next to the other side, which is filled with Scooby Snacks. Scooby-Doo can't resist eating them, and the Joker and Penguin leave to hunt down treasure. However, Batman and Robin arrive to stop Scooby-Doo before he can doom his comrades. After a brief safety announcement about sharks, the Dynamic Duo free the Mystery Gang and explain that the Joker and Penguin learned that the theater once belonged to Benny "Bulldog Benson", a notorious criminal who hid a fortune in the theater before he died. The theater is due to be torn down so they're looking for the money. Fred has a plan, but Shaggy and Scooby-Doo head for the Batmobile. Batman assures them that they'll be safe... as long as they follow the plan.

The Joker and Penguin have no luck finding the hidden money. The lights go out and the ghost of Bulldog appears, thanks to a smoke machine, lights, mirrors, and Scooby and Shaggy in a trench coat. They call upon the villains to surrender, but accidentally drop their coat. Batman and Robin swing in and the villains run away in terror, Bat-Mite gets bored with the chase and notes that in the 60s, the heroes weren't allowed to punch people. With a little fifth-dimensional magic, heroes and villains are soon engaged in a fistfight. When it looks like the heroes will be defeated, Bat-Mite gives Scooby and Shaggy fighting abilities as well, and the villains are quickly overwhelmed. Batman entangles the Penguin in his Batrope, while the Joker is hit in the head with an accordion by... Weird Al, who explains that the Joker dropped him down a trapdoor into an old elevator, and Bulldog's bags of cash broke his fall. Batman promises that millionaire Bruce Wayne will match the money to help Al build a Polka and Novelty Song Hall of Fame, and the Mystery Gang polka to celebrate while Batman and Robin quietly slip away.
Bat-Mite finishes his story and explains that his bat-trophy room goes on forever. He invites the audience to join him again, and then tunes into "Legends of the Dark Mite!"

This is a reference to the two episodes in 1972's "New Scooby-Doo Movies" series where Batman and Robin teamed up with the Scooby Gang (2nd "The Dynamic Scooby-Doo Affair" and 15th "The Caped Crusader Caper" episodes) to shut down a counterfeiting operation and kidnapping of Professor Flaky by Joker and Penguin.

The Scooby-Doo sequence contains several quite deliberate animation errors, evoking the era in which the inspirations were made.

In one sequence, both Shaggy and Robin punch Penguin out at the same time, which may be a reference to how, in the original Scooby-Doo episodes, both characters were voiced by Casey Kasem. In fact, Kasem did Robin's voice for almost twenty years, while he did Shaggy's for almost forty.